Adhesives for wall coverings are typically based on pre-pasted CMC and Starch, CMC+Starch, or pressure sensitive adhesive formulations. For example, U.S. Pat. No. 4,355,074 discloses the use of a swellable polymer, NaCMC, as an adhesive.
However, conventional wall coverings do not currently provide adhesion and repositionability by spraying water to the wall surface.
Alternative adhesive compositions are known in the patent literature. Thus, U.S. Pat. No. 4,361,452 discloses an aqueous adhesive used in wall coverings. The patent provides for adhesives containing water insoluble but water absorbable polymeric micro-particle having a diameter in the range of 0.2 and 6 microns when dry. It is suggested that wall paper adhesives formulated from water swellable but water insoluble synthetic polymeric materials will give good bond strength and that it is possible to reduce the viscosity of the coating formulation to levels acceptable for wallpaper adhesives by including water soluble polymeric material in the composition.
U.S. Pat. No. 4,476,190 discloses an adhesive layer for a wall paper which comprises cationic and anionic water absorbent particles that are insoluble in water in order to produce an adhesive layer that is initially not in contact with the wall surface until the wall paper is pressed into the wall and the water absorbent particles are crushed. The adhesive then becomes in contact with the wall and the wall paper is adhered to the wall. The document teaches that the polymeric materials can be made swellable by the inclusion of N,N1-methylene bisacrylamide.
Due to the chemical nature of the polymers used in U.S. Pat. No. 4,476,190, they must be dispersed to the paper substrate by adding them directly into the paper using and organic dispersant, such as kerosene. The carrier must be sufficiently volatile so as to evaporate without water as water will cause the particles to swell prematurely.
WO2000/031201 discloses a self-adhesive wall covering that includes a moisture bather. The self-adhesive wall covering is composed of a dry adhesive with elastic, fragible micro-particles suspended in it. The micro-particles may include solid or hollow glass particles whose largest size is larger than the thinnest portion of the adhesive layer. This insures that at least some of the particles project above the adhesive layer. When the wall paper is in place is pressed into the wall, the spheres break and the adhesive is activated by the pressure and the fact that a large portion of the paper surface has adhesive in contact with the wall. The crushable particles will be permanently deformed when pressed against the wall.
The moisture bather protects the wall paper from high humidity environments but not from water used to activate the adhesive. The known wall covering is not activated by water.
Further art is represented by EP 0194857, U.S. Pat. No. 4,639,395, WO 9527826, WO 2005095712 and U.S. Pat. No. 3,883,269.
As apparent from the foregoing overview, the wall covering adhesives proposed so far are deficient in many aspects. The compositions suggested are complex, requiring a number of components, and elaborate techniques are needed for application of the adhesive layer on the back side of the wall covering. Further, the studied compositions contain components which are irreversibly changed after application of the wall covering against the desired surface which makes it difficult to remove wall coverings once they have adhered to the surface.
A further problem is the lack of properly working moisture barriers which will allow for wetting of the adhesive and subsequent efficient drying, while still protecting the substrate layer of the wall covering.